1. Technical Field of the Invention
The present invention relates generally to a spark plug for internal combustion engines which may be employed in automotive vehicles, cogeneration systems, or gas feed pumps, and more particularly to an improved structure of such a spark plug designed to shape or orient a vortex stream of air-fuel mixture, thereby ensuring the stability of ignition of air-fuel mixture in a combustion chamber of the engine.
2. Background Art
Japanese Patent First Publication No. 11-3765 (U.S. Pat. No. 6,846,214 B1) discloses a typical spark plug for internal combustion engines which includes a metal shell with an external mounting thread, a porcelain insulator retained in the metal shell, a center electrode retained inside the porcelain insulator, and a ground electrode welded to the metal shell to define a spark gap between itself and the top of the center electrode.
The above type of spark plug works to produce a sequence of sparks within the spark gap to ignite an air-fuel mixture, thereby creating flame which will grow to induce the detonation of the mixture.
Usually, after entering a combustion chamber of the internal combustion engine, the air-fuel mixture creates a vortex stream which may flow into a pocket defined between the metal shell and the porcelain insulator of the spark plug, which forces an initial flame, as produced around the spark gap, into the pocket so that it is extinguished. This results in a failure in burning the air-fuel mixture completely.
Especially, direct-injection engines are so designed as to charge an air-fuel mixture into the combustion chamber at a high velocity in order to stir the air and fuel and, thus, have a greater concern about the facilitation of extinguishing of the flame of the air-fuel mixture.